In general, a storage system is configured to cache data (host data) being read from a storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive) into a cache memory (CM) in order to expedite a response to a read request from a host computer so that, when a read request targeting the identical host data to be read is received thereafter, the host data on the CM can be returned to the host computer without accessing the storage device.
The storage system includes a controller which controls access to the storage device and is redundant in general. Such storage system secures as much area as possible by using a plurality of CMs included in a plurality of controllers as the cache for the host data, whereby a hit rate (CM hit rate) of the host data can be increased.
In such case where the plurality of CMs in the plurality of controllers is used, it is required that the plurality of controllers share information (hereinafter referred to as cache management information) indicating correspondence between the CM and a storage destination of data on the CM (such as an assigned number, an address, and a data size of a logical volume (LDEV)). There is known a method in which the cache management information is synchronized among the plurality of controllers by using a shared memory (see PTL 1, for example).